If there is one set of conditions that you'd like to set as your default view in the Purchase Order section, you can 'save' the view for future use.
As an example, to filter out FBA shipments from your Purchase Order overview, click on Filters > Warehouse to show a list of warehouses that will be the destination for your shipment.
From the dropdown, click on your non-Amazon warehouse to filter out Amazon shipments.
To set this as your default view, you can do this while naming your filter. First click on Filters > Save Filter As.
Then select your filter name and set as default if desired.
If you would like to set a previously saved filter as a default, click on Filters, click the name of the filter, then select 'Use filter <your filter name> as the default'.